1. Field of the Invention
The present invention relates to an electric motor having a rotation detection sensor and, more particularly, to an improvement in mounting a rotary member of a rotation detection sensor on a motor rotary shaft.
2. Related Art
It is known to provide a rotation detection sensor in an electric motor. As shown in FIG. 22, this type of motor 21 has an annular permanent magnet 24 fixed around a rotary shaft 23 of an armature 22, so that it operates as a rotary member of the rotation detection sensor. The magnet 24 is bonded to a metal bushing 25 by an adhesive bond, and press-fitted on the rotary shaft 23 together with the bushing 25.
This arrangement requires a high press-fitting precision, so that the busing 25 is fitted fixedly on the rotary shaft 23. That is, a through hole 25a of the bushing 25 and the rotary shaft 23 must be machined with high precision. Further, it is necessary to bond the magnet 24 and the bushing 25, and to dry the adhesive bond thereafter.
Further, a resin washer 27 is disposed between the magnet 24 and a bearing 26 supporting one end of the rotary shaft 23 therein, thereby preventing the magnet 24 from sliding on the bearing 26 directly. This results in increases in the number of component parts, in the number of production processes, and in production cost.